The invention generally relates to the sampling of vapors and their delivery to sensory elements in various chemical sensors or sensor arrays. Usually any sensor for detecting vapors, especially low pressure vapors, requires a sampling and delivery system. The most general sampling and delivery method is vapor pumping through a flow channel where the sensory element(s) is placed. The interaction of analyte vapors with the sensory element affects its physical-chemical properties (e.g., electrical conductivity, optical absorption, etc.), and their changes can be detected followed by analyte vapors identification and quantification.
To increase the sensitivity to analyte vapors, porous materials with a large surface area are employed. The porous medium can be sensitive itself or can be infiltrated with a sensory material. The major problem here is the vapor permeability through the pores, in which the topology can be branch-like (or pores can be partially clogged), making vapor diffusion inside the pores difficult. This factor can seriously detriment the sensor performance reducing its high sensitivity that is expected from the large surface area. If the average pore size of the sensory membrane is small (less than 1-2 μm), the pump cannot provide effective vapor delivery through the pores because of the low flow rate (flow normal to the membrane surface). Increasing the flow rate will require higher pump power and could result in the membrane breakdown.
Therefore, the sensory membrane should be fixed so that it will provide a flow parallel to its surface. In such a configuration, despite the absence of the flow rate limitation, vapors still cannot penetrate deep inside the membrane. Therefore, there is a need in the delivery method, which combines the parallel vapor flow with an effective permeability mechanism through the porous structure.